Eurostar.com
The official Eurostar site has a journey planner and other
useful information, but it can be maddening to use. (Tip: Select the "UK" as
your country of residence if you live overseas. Fares will be converted into
your local currency when you charge to your credit card.)

Rail
Europe: Eurostarour partner
If you live in the U.S., you may find Rail
Europe easier to deal with than Eurostar, although bargain fares don't
always show up on its pages.

Background information and photos

Wikipedia:
Eurostar
The online encyclopedia's article is packed with facts, figures, and trivia.

Le Shuttle (car train)

Eurotunnel
Load your car, motorcycle, camper, or caravan on Le Shuttle for a 35-minute rail
journey under the English Channel between Folkestone, England and Coquelles,
France. (If you're traveling with a group, you can even reserve a spot for your
tour bus.)